The evolution of crystalline structure induced by heat treatment and high pressure torsion (HPT)
deformation and its influence on the magnetic properties of amorphous and partially crystalline
Hf2Co11B ribbons were investigated. Slight improvement in thermal stability of the as-quenched sample
after deformation was observed as indicated by the shift of the first crystallization peak from 592 to
598 C. Plastic deformation of the initially annealed partially crystalline alloy led to its amorphization, as
confirmed by X-ray diffraction (XRD). However, the presence of small volume fraction of needle-like
nanocrystals was indicated by transmission electron microscopy (TEM). The annealed sample subjected
to high pressure torsion was characterized by the reduced coercive field, from 0.7 to 0.2 kOe, while
the subsequent reannealing of the deformed sample enhanced the coercivity up to 1.3 kOe. Transmission
electron microscopy analysis revealed the existence of nanocrystals with large lattice constant of 8 Å
characteristic of Hf2Co11 phase. Magnetic measurements also confirmed that some nanocrystals of the
hard magnetic phase were present in the sample after deformation, indicating their importance for maximization of coercivity. The isolation of this quite elusive phase is clearly linked to magnetic performance and the method combining severe plastic deformation (SPD) and heat treatment was found to allow tuning of the structure and improving the hard magnetic properties.